1is2many
XS650 Enthusiast
can the camshaft be put in "backwards" as to have the points on the right side of the motor instead of the left side? i dont think it will change the valve opening process but i'm not sure.
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camshaft question
- Thread starter 1is2many
- Start date
mrriggs
XS650 Junkie
I don't think it will matter as far as the lobes are concerned. I've held the two halves of a cam side by side and they look identical.
The ATU would be a problem as it would retard the timing rather than advance it.
The ATU would be a problem as it would retard the timing rather than advance it.
robear54
XS650 Member
I've been having trouble with my 1980 xs, after many swaps with another bike I have finally noticed that my camshaft is installed backwards. The motor was rebuilt by the PO and the problem starts between 4500-5000rpm's.
It just falls flat on its face and will not rev any higher without alot of backfiring. From looking at a spare cam, the lobes do not look symmetrical and I am thinking that I have found the problem. Unfortunately I have had this feeling before. Everthing electrical has been swapped, carburators swapped. Anyway, from this experience and the fact that you would have to drill and tap two holes to secure the point plate, and I agree with mrrigs about the advance issue. Why do you want the points on the right side?
It just falls flat on its face and will not rev any higher without alot of backfiring. From looking at a spare cam, the lobes do not look symmetrical and I am thinking that I have found the problem. Unfortunately I have had this feeling before. Everthing electrical has been swapped, carburators swapped. Anyway, from this experience and the fact that you would have to drill and tap two holes to secure the point plate, and I agree with mrrigs about the advance issue. Why do you want the points on the right side?
Are you asking a question from a guy that posted 5 years ago, and expecting an answer?
littlebill31
Smells of Raw Fuel
You can run a cam shaft backwards as long as you have a TCI ignition unit, not points.
It will run fine.
And honestly, if the PO "rebuilt" the engine, he didn't follow simple instructions by putting the cm in backwards. God knows what else he did wrong.
.....
It will run fine.
And honestly, if the PO "rebuilt" the engine, he didn't follow simple instructions by putting the cm in backwards. God knows what else he did wrong.
.....
robear54
XS650 Member
New to the site and didn't notice when it was posted. As far as running the cam backwards, I disagree. The lobes are not symmetrical, so the open ramp and the close ramp are different. If the cam is installed backwards it will run fine up to about 4500 rpm, after that it starts breaking up as I mentioned in my post. I just swapped the cam around today and now it runs great all the way to red line. I've spent more time than I like to admit chasing this issue but am very happy that it is finally resolved. Thanks for the heads up on noticing the date, I had been reading several different post and obviously picked the wrong one to reply to.
I've been on these XS650 web sites for about 10 years now, and every 2 to 3 years we hear about guys with camshafts installed backwards. Usually the bad deed is discovered before they run the engine. Interesting that you have run the engine and post the proof that the engine only works up to 4500 rpm.
It is scary that some of the lads working on these bikes can and do make fubars. Congrats on sorting it out and getting the engine back to normal!
It is scary that some of the lads working on these bikes can and do make fubars. Congrats on sorting it out and getting the engine back to normal!
^I wonder if his cam has been ground. He says intake and exhaust are different and Mr. Riggs says they are the same.
Ok, I just looked it up and the spec for the height of the exhaust cam is .002" taller than the intake. But the tolerance for both is +-.002" which means the intake could be .002" taller than the exhaust and both would still be in spec! Strange. Duration is the same for both, 284 degrees.
Ok, I just looked it up and the spec for the height of the exhaust cam is .002" taller than the intake. But the tolerance for both is +-.002" which means the intake could be .002" taller than the exhaust and both would still be in spec! Strange. Duration is the same for both, 284 degrees.
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The cam lobes won't look symmetrical because of the angular sweep of the rotating rocker's pad. The valve motion will still be symetrical. However, with the cam backwards, the cam timing will be strange. Ex, the right cyl exhaust lobe would now be driving the left cyl's intake, in reverse. If you use this timing diagram, flip it over (left to right), and label the exhaust as intake, and intake as exhaust, and relabel open as close, close as open, you'll get the valve timing for a backwards installed cam. Close enuff to run, but not well...
robear54
XS650 Member
Thanks for all the information, when I removed the cam, the notch was at 12:00 like it is supposed to be, just on the wrong side. In my research on this I found a chart that listed rotation in degrees vs travel of valve stem for each valve. I don't remember the numbers (and I can't findthe file again) but I noticed the degrees to cause the valve to open from 0 deflection to .050" was more than it was to close the same valve from .050" to 0. That is why I thought there was a difference between the open and close side of the lobe.
Thanks again
Thanks again
Wasn't this the trick allowing a head installed (backwards) with the carbs in front? Guess maybe it was a "show bike".... But someone had a drag bike with a reversed head. maybe they had the cam ground to correct the ramps.
robear54
XS650 Member
Yes, that was the chart I found before, thanks. I need to do a better job of saving links, my memory isn't what it used to be. After looking at the chart again I see I misunderstood what it was showing.
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Some interesting stuff in that link!
robear54
XS650 Member
Back to the drawing board, when I went for a test ride today it was still stumbling between 4 and 5k rpm. I think it is better than it was but obviously I still have issues. Will update later in the week when I get time to get back to it.
Ouch that's gotta be disheartening Man! 4-5 k is about where you are out of the needle jet and on the mains.
littlebill31
Smells of Raw Fuel
Do you have stock exhaust?
What carbs?
What carbs?
robear54
XS650 Member
Stock bs34 cv carbs. PO put alot of Mikes xs stuff on these bikes,I have 2 1980 models that I bought from him.
Jet kit with 135 main, adjustable needle and 3mm drilled out slide
Pod air filters
2 into 1 exhaust with a pretty restrictive megaphone (headpipes 1 3/8" id I think)
Started with needle clip in the third slot from the top, 135 main jet, spark plugs looked rich.
Now I'm down to 127.5 main jet electrode on plug tan, insulator still dark, need to get a new set of plugs.
The only reason I found the cam to be reversed was because I was going to install a pamco ignition kit
To rule out spark issues. When I was checking the timing with my light I had a good strobe until I increased the throttle and then it became intermittent . Coil, stator,ignitor all swapped with other bike with no change. The only thing I didn't change was the rotor (magnet seems good).
I have gone back and forth thinking it is a carb issue, then spark, then exhaust.
I think I'm going to continue with the pamco install, that should eliminate spark one way or the other.
I have the 14-0913 pamco kit which includes everything and reuses nothing from stock.
A little more than you asked for, lucky for you I'm tired of typing, any suggestions welcome but I can't work on the bike again until Friday.
Jet kit with 135 main, adjustable needle and 3mm drilled out slide
Pod air filters
2 into 1 exhaust with a pretty restrictive megaphone (headpipes 1 3/8" id I think)
Started with needle clip in the third slot from the top, 135 main jet, spark plugs looked rich.
Now I'm down to 127.5 main jet electrode on plug tan, insulator still dark, need to get a new set of plugs.
The only reason I found the cam to be reversed was because I was going to install a pamco ignition kit
To rule out spark issues. When I was checking the timing with my light I had a good strobe until I increased the throttle and then it became intermittent . Coil, stator,ignitor all swapped with other bike with no change. The only thing I didn't change was the rotor (magnet seems good).
I have gone back and forth thinking it is a carb issue, then spark, then exhaust.
I think I'm going to continue with the pamco install, that should eliminate spark one way or the other.
I have the 14-0913 pamco kit which includes everything and reuses nothing from stock.
A little more than you asked for, lucky for you I'm tired of typing, any suggestions welcome but I can't work on the bike again until Friday.
bighairyralph
XS650 Addict
Ditch the pods. They're causing the slide to flutter. If they're crap filters they could be covering a vacuum port on the carb too - which will make it way worse. It seems like most guy have better luck with the UNI filters.
